A battery-powered device such as a power tool can be used cordlessly, for example, at a construction site, when a detachable battery pack containing rechargeable batteries is provided. When the remaining capacity of a battery pack is low, the battery pack is placed in a battery pack charger and recharged.
FIG. 28 through FIG. 34 show an example of such a battery pack. FIG. 28 is an external perspective view of the battery pack, FIG. 29 is an exploded perspective view of the battery pack in FIG. 28, FIG. 30 is a perspective view of the battery holder 70X in FIG. 29, FIG. 31 is a perspective view of the battery holder in FIG. 30 with the pack circuit board 74X removed from the battery holder 70X, FIG. 32 is a vertical cross-sectional view of the battery holder 70X from line XXXII-XXXII in FIG. 30, FIG. 33 is an enlarged cross-sectional view of FIG. 32, and FIG. 34 is a perspective view of the power lead. The battery pack in these drawings contains a battery holder 70X in which a plurality of secondary batteries have been connected, and a pack circuit board 74X on which electronic circuitry for monitoring the batteries has been mounted. Lead wires and battery lead plates 80X are used to wire the pack circuit board 74X and the secondary batteries. The end faces of the secondary batteries are connected using battery lead plates 80X, and lead wires are used to connect the battery lead plates 80X to the pack circuit board 74X. A thick-diameter power lead 85X is used to wire a high-voltage output line.
However, the thick power lead 85X is wired in a tight space, and is not easy to solder. It is difficult to bend the power lead in the confined space as indicated by the solid arrows in FIG. 33 and FIG. 34. Even when the power lead 85X can be soldered, the power lead 85X can still move freely after being wired. For example, the lead wire sometimes moves in the direction indicated by the broken line arrow in FIG. 33. Therefore, when the battery pack is subjected to vibrations or impacts, the power lead 85X moves inside the battery pack. The lead wire may be worn down and exposed by friction, become disconnected, or come into contact with a component having a different voltage and short-circuit.
To resolve this problem, the wiring of the pack circuit board using metal lead plates has been considered. However, a large amount of space is required to arrange a circuit board using lead plates, and the conductivity is poor because thin plates are used. As battery packs get smaller, there will be increasing demand for reliable wiring in smaller wiring spaces. However, a wiring structure able to meet this demand has not yet been developed.
For an example, see Japanese Laid-open Patent Application No. 2010-146879.